Laboratory incubators are generally constructed in a rectangular box-like configuration. The chamber of the incubator may have a water jacket, a so-called "wet" incubator, in which water is heated to maintain the inside of the incubator at a substantially constant, predetermined temperature such as 37.degree. C. (body temperature). Dry incubators are also used. Both types of incubators have at least one door which forms one side of the incubator chamber and provides access to the interior of the incubator chamber. In some incubators there are two doors, the outer door being metal and the inner door containing a light, such as a pane of glass, for viewing specimens in the incubator chamber without disturbing the thermal equilibrium of the incubator environment. In those incubators in which there is only one door, it may include the light.
Heretofore, incubator doors, although an integral part of the chamber construction, have not included any satisfactory means for heating the incubator chamber. Consequently, all of the heat required has been provided by radiant type, open-coil heaters in the dry incubators or by thermal transfer from the water jacket through the remaining five sides (the three vertical sides, the top and the bottom) of the wet incubators, or by use of an open-coil heater in the outer doors of some incubators. None of these designs has achieved the high level of uniformity in incubator temperature which the present invention has achieved through the use of a heated door and particularly a heated glass light in an incubator door.
Although heated lights have been used in other applications, e.g. as automobile window defrosters, the particular heated glass light door construction herein disclosed is not known nor has any heated glass door been used in an incubator for laboratory use.